1. Field of the Invention:
The invention is directed to the field of subsurface trenching for the installation and removal of various utility items such as electrical cable, conduit, water pipes; sewer pipes and the like where same must be mounted below surface for their protection from the environment and populace and to hide their otherwise unsightly appearance.
2. Description of the Prior Art:
The usual method for the laying or removal of utility items such as electrical cables, conduit, water pipes, sewer pipes and the like is to cut or dig a straight sidewall trench of the appropriate depth, lay the cable, conduit or pipe at the trench bottom and cover it up with the soil removed during the trench formation.
When the land is undeveloped, that is has no structures, plantings, parking lot, etc., upon it, it is a simple matter to cut or dig the trench using mechanized equipment such as trenchers, front loaders, bulldozers or the like, or, if desirable, to manually dig the trench.
However, when the land has been improved as by the building of structures upon the land surface or the surface has been covered as in a parking lot or where gardens and plantings have been placed on the land, installation, removal and/or replacement of utility items is both slow and expensive. Often, space and access limitations prevent any methods other than manual trenching from being used and in addition to the work itself, there is the disruption of land use and the expense of restoring the trenched area to its former appearance.
In an effort to minimize surface disruption and minimize the costs of surface reconstruction, it has been suggested that a device be constructed to burrow beneath the surface of land and create a bore into which cable, conduit, pipe or the like could be inserted without disturbing the surface of the land or those structures or details thereon. A first type of device was created to permit the replacement of electrical cables and used those cables to guide their movement through the soil which was removed by means of one or more fluid jets. The old cable was pulled from the bore and a new one inserted. A tool of this type is shown in U.S. Pat. No. 4,385,667 issued May 31, 1983 and in U.S. Pat. No. 4,403,667 issued Sept. 13, 1983.
Although this type of device works well for previously installed electrical cable replacement, it is not suitable for new cable installation because there is no cable to follow and thus no means to independently guide the tool.
U.S. Pat. No. 4,306,627 issued Dec. 22, 1981 shows and describes a tool which can be used for a new installation. A rotating fluid jet drilling nozzle is advanced by a pipe string in much the same manner as a rock drill is employed to dig oil or gas wells. Despite mechanisms to control the position of the nozzle, as is shown in U.S. Pat. No. 4,674,579 issued June 23, 1987, it is still difficult to steer the boring head mounted at the end of a generally rigid pipe string required to push and advance the boring head.
The use of a totally independent tool such as shown in U.S. Pat. No. 3,326,008 issued June 20, 1967 presents different problems. Because it must rely upon only its own drilling head, it is limited as to how fast it can advance and the type of subsoil it can burrow through. Also, since it carries internally the cable it lays, it is limited in its utility. Also, its inability to reverse and retrace the bore it makes limits its ability to draw new cable, conduit or pipe back through the bore. The device must always exit the soil to be recovered and used again.